The preparation of styrenic block copolymers is well known in the art. Generally, styrenic block copolymers (“SBC”) can comprise internal polymer blocks and terminal end polymer blocks comprising chemically different monomer types thereby providing particular desirable properties. As an example, in a more common form, SBC's may have internal blocks of conjugated diene and external blocks having aromatic alkenyl arenes. The interaction of the differing properties of the polymer blocks allow for different polymer characteristics to be obtained. For example, the elastomer properties of internal conjugated diene blocks along with the “harder” aromatic alkenyl arenes external blocks together form polymers which are useful for an enormous variety of applications. Such SBC's can be prepared through sequential polymerization and/or through coupling reactions.
It is known also that SBC's can be functionalized in order to further modify their characteristics. An example of this is the addition of sulfonic acid or sulfonate functional groups to the polymer backbone. One of the first such sulfonated block copolymers is disclosed, for example, in U.S. Pat. No. 3,577,357 to Winkler. The resulting block copolymer was characterized as having the general configuration A-B-(B-A)1-5, wherein each A is a non-elastomeric sulfonated monovinyl arene polymer block and each B is a substantially saturated elastomeric alpha-olefin polymer block, said block copolymer being sulfonated to an extent sufficient to provide at least 1% by weight of sulfur in the total polymer and up to one sulfonated constituent for each monovinyl arene unit. The sulfonated polymers could be used as such, or could be used in the form of their acid, alkali metal salt, ammonium salt or amine salt. According to Winkler, a polystyrene-hydrogenated polyisoprene-polystyrene triblock copolymer was treated with a sulfonating agent comprising sulfur trioxide/triethyl phosphate in 1,2-dichloroethane. The products are described as having water absorption characteristics that might be useful in water purification membranes and the like.
More recently, US 2007/0021569 to Willis et al. disclosed the preparation of sulfonated polymer and inter alia illustrated a sulfonated block copolymer that is solid in water comprising at least two polymer end blocks and at least one saturated polymer interior block wherein each end block is a polymer block resistant to sulfonation and each interior block is a saturated polymer block susceptible to sulfonation, and wherein the interior blocks are sulfonated to the extent of 10 to 100 mol percent. The sulfonated block copolymers are described as having a high water vapor transport rate while at the same time having good dimensional stability and strength in the presence of water, and as being therefore valuable for many end use applications, especially where the combination of good wet strength, good water and proton transport characteristics, good methanol resistance, easy film or membrane formation, barrier properties, control of flexibility and elasticity, adjustable hardness, and thermal/oxidative stability are important.
Additionally, WO 2008/089332 to Dado et al. discloses a process for preparing sulfonated block copolymers illustrating, e.g., a process which involves providing a precursor block copolymer having at least one end block A and at least one interior block B wherein each A block is a polymer block resistant to sulfonation and each B block is a polymer block susceptible to sulfonation wherein said A and B blocks are substantially free of olefinic unsaturation; and reacting the precursor block copolymer with an acyl sulfate in a reaction mixture further comprising at least one non-halogenated aliphatic solvent to form a sulfonated block polymer. The product obtained in the process is described as comprising sulfonated polymer micelles and/or other polymer aggregates of definable size and distribution, as would be characteristic of polymer micelle structures.
It has also been reported that sulfonated polymers may be neutralized with a variety of compounds. U.S. Pat. No. 5,239,010 to Pottick et al. and U.S. Pat. No. 5,516,831 to Balas et al., for example, indicate that styrene blocks with sulfonic acid functional groups may be neutralized by reacting the sulfonated block polymer with an ionizable metal compound to obtain a metal salt.
Additionally, US 2007/0021569 to Willis et al. indicated the at least partial neutralization of the sulfonated block copolymer with a variety of base materials including, for example, ionizable metal compounds as well as various amines. It was further proposed that the sulfonated block copolymer may be modified by hydrogen bonding interaction with a base material which, while not sufficiently strong to neutralize the acid centers of the sulfonated block copolymer, is strong enough to achieve a significant attraction to the block copolymer via a hydrogen bonding interaction.